If you change the seat you'll have to replace the lock (and then all locks). 2000 => new tank and seat. Next time also watch for newer FI tanks, they're different. AFAIK, a 2001 M900 is only FI and wouldn't work either.
how about buying a pre-2000 stock seat (one on ebay right now still at $20), and attaching to its underside the latch peg off my current (non-fitting) seat? The swap shouldn't be too hard, if all else fails by drilling the little plate onto the older seat. Then i could use the older seat without changing the locks..
but did the frame change as well (such that the plastic seat tabs don't fit under and attach in place in the same way)?? I can post pics if it helps..
I have a stock seat from a 97 and still have the seat latch that went with it. Plus I'm close enough to San Francisco that you could come check things out first to see if it would work. I can make you a good deal on it.
I would call and visit Munroe and Desmoto. They will most likely have a few lying around to compare or even try on. They will probably be able to tell you also what needs to be done while having it on hand.